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TRANSCRIPT
Welcome to…
General Ecology
PCB 4043
with Dr. Bill Tyler
1 Introduction:
The Web of Life
Chapter 1 The Web of Life
• Case Study: Deformity and Decline in Amphibian
Populations
• CONCEPT 1.1 Events in the natural world are
interconnected.
• CONCEPT 1.2 Ecology is the scientific study of
interactions between organisms and their
environment.
• CONCEPT 1.3 Ecologists evaluate competing
hypotheses about natural systems with observations,
experim
• Case Study Revisited
1 Introduction: The Web of Life
• Case Study: Deformity and Decline in Amphibian Populations
• Connections in Nature
• Ecology
• Answering Ecological Questions
• Case Study Revisited
• Connections in Nature: Mission Impossible?
Case Study: Deformity and Decline in Amphibian Populations
• 1995, elementary and
middle school students
discovered deformed
leopard frogs
• High incidence of
deformities in some 60
species of amphibians
Declining populations of
amphibians worldwide
since late 1980s
Figure 1.1 Deformed Leopard Frogs
Figure 1.2 Amphibians in Decline
Deformity and Decline in Amphibian Populations: A Case Study
• Amphibians are “biological
indicators” of environmental
problems.
Skin is permeable; pollutant
molecules can pass through easily.
Eggs have no protective shell.
They spend part of their life on
land and part in water—exposed to
pollutants and UV in both
environments.
Examples of some
amphibian deformities in
northern leopard frogs
http://www.nwhc.usgs.gov/disease_information/amphibian_malformation_and_decline/index.jsp
http://www.environment.gov.au/soe/2006/publications/drs/indicator/70/index.html
Numbers of amphibian species worldwide and threatened
Introduction
Humans have enormous impact on the planet Transformed nearly half of land;
even vast oceans
Must understand how natural systems work
Ecology Scientific study of how
organisms affect — and are affected by — other organisms and their environment
Interactions between organisms and their environment (includes other organisms)
http://www.learner.org/courses/envsci/visual/img_med/past_pop_growth.jpg
http://www.satyamag.com/sat.site.images/clear-cut.jpg
Clear cutting of timber
Introduction
Ecology is an interdisciplinary approach
ECOLOGY
Evolutionary
Ecology
Physiological
Ecology
Microbial
Ecology
Soil
Ecology
Ecosystem
Ecology
Landscape
Ecology
Population
Ecology
Community
Ecology
Behavioral
Ecology
Global
Ecology
Plant
Ecology
Animal
Ecology
Applied
Ecology
Restoration
Ecology
Conservation
Biology
Wildlife
Biology
Connections in Nature
• Even species that do
not interact directly can
be connected by shared
environmental features
• Ecologists ask
questions about the
natural world to
understand these
connections
Concept 1.1: Events in the natural world are
interconnected.
http://www.mercuryinschools.uwex.edu/lib/images/curriculum/florida_food_web.jpg
Florida trophic interactions
Connections in Nature
Observations of Pacific
tree frogs suggested that
parasites can cause
deformities
Sessions & Ruth, 1990:
Implanted glass beads
mimics effect of Ribeiroia
ondatrae cysts, a
trematode flatworm, in
different frog species
(Xenopus)
http://northislandexplorer.com/amphibians/pacifictreefrog.jpg
http://www.sci.sdsu.edu/classes/biology/bio588/Metacercaria20.gif http://www.stockpix.com/image/2857.jpg
Connections in Nature
Johnson et al:
Deformities of Pacific tree frogs occurred
only in ponds which also had an aquatic
snail, Helisoma tenuis, the intermediate
host of the parasite
All frogs with deformed limbs had
Ribeiroia cysts.
http://www.stockpix.com/image/2890t.jpg
Figure 1.3 The Life Cycle of Ribeiroia
Connections in Nature
A controlled experiment to test
hypothesis that Ribeiroia
parasites caused deformities
(Johnson et al, 1999)
Tree frog eggs were exposed to
Ribeiroia parasites in the lab
Four treatments: 0 (control
group), 16, 32, or 48 Ribeiroia
parasites
As parasite load increased,
survival decreased and
deformities in survivors
increased
Supported by other field work
Figure 1.4 Parasites Can Cause Amphibian Deformities
Connections in Nature
Kiesecker (2002) conducted a
field experiment:
Six ponds, three with
pesticide contamination
Added tadpoles to cages
Six cages in each pond
Three with mesh size
allowing parasites to enter
Three with mesh blocking
parasites (“exclusion cage”)
Figure 1.5 Do Ribeiroia and Pesticides Interact in Nature? (Part 1)
Figure 1.5 Do Ribeiroia and Pesticides Interact in Nature? (Part 2)
Mesh blocking parasites Mesh allowed entry of parasites
Pesticides alone had no effect on deformities
• Pesticides significantly weakened resistance to parasites
Connections in Nature
Next hypothesis: Pesticides
decrease frog’s ability to resist
parasite infection (Kiesecker,
2002)
Another lab experiment: Infected
tadpoles reared in presence of
pesticides
had fewer white blood cells
(indicating a suppressed
immune system) and…
higher rate of Ribeiroia cyst
formation
Figure 1.6 Pesticides May Weaken Tadpole Immune Systems (Part 1)
Experiment with two controls (a & b)
a) Control = only parasites
b) Parasites & solvent only (check for
effect of solvent [“sham”] no
effect)
c) Parasites & low pesticide in solvent
d) Parasites & high pesticide in
solvent
Connections in Nature
Unintended effects via
interconnections:
• Synthetic pesticide use
began in 1930s and has
increased dramatically since
Amphibian exposure to
pesticides has also increased.
Any action (increased pesticide
use by people) can potentially
have unanticipated side effects
(more frequent deformities in
amphibians).
http://www.fs.fed.us/ne/delaware/biotrends/trends79.JPG
Schmitt CJ. 1998. Environmental
Contaminants. Pages 131-165 in Mac
MJ, Opler PA, Puckett Haecker CE,
Doran PD. Status and trends of the
nation's biological resources. U.S.
Department of the Interior, U.S.
Geological Survey, Reston, Va.
Connections in Nature
Fertilizer use may also be a
factor:
Fertilizer in runoff to ponds
increases algal growth
Snails that harbor Ribeiroia
parasites eat algae
Greater numbers of snails
result in greater numbers of
Ribeiroia parasites
http://cropsoil.psu.edu/extension/facts/img/af38afig2.jpg
http://msnbcmedia2.msn.com/j/msnbc/Components/
Photos/050614/050614_algae_hmed_6a.hmedium.jpg
Long-term
impacts (algal
blooms) seen on
lakes from
fertilizer, manure
http://www.msnbc.msn.com/id/8214501/
Connections in Nature
Many human actions have also
increased human health risks
Damming rivers in Africa
increases habitat for snails that
carry schistosomiasis
New diseases (e.g. AIDS, Lyme
disease, Hantavirus, Ebola, &
West Nile fever) may be related
to human activities
Humans expanding into more
wilderness areas, contacting
more animal hosts increases
exposure to “novel” viruses
http://www.fao.org/docrep/005/ad002e/AD002E05.gif
Schistosomiasis in Africa
http://www.universityscience.ie/imgs/scientists/shistosomiasis.gif http://www.wikieducator.org/images/4/4c/Schistosomiasis.jpg
Figure 1.7 Rapid Spread of a Deadly Disease
West Nile virus spread from New York
City (point of entry) to 45 states.
Birds are primary host and
mosquitoes are vectors
Mammals (including humans) are
“dead-end” carriers
Figure 1.7 Rapid Spread of a Deadly Disease
Ecology
Ecology is a branch of biology that combines
information about organisms and the physical world
Environmental science is even more interdisciplinary
incorporates concepts from
the natural sciences (ecology and physical sciences)
and…
the social sciences (economics, policy/law, ethics)
focuses on solutions to environmental problems
Concept 1.2: Ecology is the scientific study of
interactions between organisms and their
environment. Jump to
Slide #43
Ecology
Early (and out-dated) ecological views:
• A “balance of nature”
natural systems are stable and tend
to return to an original state after
disturbance
• Each species has a distinct role to play
in maintaining that balance
Ecology
Ecologists now recognize that
ecological interactions are
much more complex...
• Natural systems do not
necessarily return to their
original state after a disturbance
(“tipping points”).
• Seemingly random perturbations
can play an important roles.
• Evidence suggests that different
species often respond in
different ways to changing
conditions.
http://io.uwinnipeg.ca/~simmons/16cm05/1116/53-11-AntarcticFoodWeb-L.gif
Concept 1.2
What Is Ecology?
One view that has stood
the test of time…
• Events in nature are
interconnected…
• A change in one part of an
ecological system can alter
other parts of that system.
http://io.uwinnipeg.ca/~simmons/16cm05/1116/53-11-AntarcticFoodWeb-L.gif
Table 1.1 (Part 1)
Table 1.1 (Part 2)
Concept 1.2
What Is Ecology?
Ecologists must select
appropriate scales of
study.
Spatial scales:
Small—soil
microorganisms
Large—atmospheric
pollutants
Temporal scales:
Short—leaf response
to sunlight
Long—how species
change over geologic
time
http://rs.resalliance.org/2010/09/28/fire-and-the-anishinaabe/
Ecology
Ecologists study interactions in
nature across many levels of
organization.
Ecological studies usually
emphasize individuals,
populations, communities,
or ecosystems.
Figure 1.8 Levels of Biological Organization (Part 1)
Figure 1.8 Levels of Biological Organization (Part 2)
Ecology
A population:
Group of individuals of a
single species that live in
a particular area and
interact with one another
A community:
Association of
populations of different
species living in the same
area.
Figure 1.9 A Few of Earth’s Many Communities
Ecology
An ecosystem is a community
of organisms plus the physical
environment in which they live
Landscapes are areas with
substantial differences, typically
including multiple ecosystems.
The biosphere:
All the world’s ecosystems
taken together
All living organisms on
Earth plus environments in
which they live
Ecology
All living systems evolve change over
time
Evolution: A change in the genetic characteristics of a
population over time
Descent with modification — organisms gradually
accumulate differences from their ancestors
Adaptation: A characteristic that improves survival
or reproduction.
http://blogs.sun.com/ChinaExperience/resource/evolution.jpg
Ecology
Natural selection Individuals within a population
with particular adaptations tend to survive and reproduce at a higher rate than other individuals
If the adaptation is heritable, the offspring will tend to have the same characteristics that gave their parents an advantage
As a result, the frequency of those characteristics may increase in a population over time
http://evolution.berkeley.edu/evolibrary/article//bergstrom_02
Figure 1.10 Natural Selection in Action
http://evolution.berkeley.edu/evolibrary/article/bergstrom_03
Natural selection is a culling or editing effect,
removing individuals without advantageous
adaptations
Figure 1.10 Natural Selection in Action
Three variables important for natural selection to operate
Variation among individuals
within the population
Heritability of the variations
Differential fitness (reproductive success) due to variation
Natural selection is an editing process…selection culls out less adapted individuals
Ecology
Ecosystem processes
Movement of energy and materials
Energy enters community when producers capture energy from an external source (usually the sun) and uses that energy to produce food
http://www.estrellamountain.edu/faculty/farabee/biobk/enflow.gif
Ecology
Net primary productivity (NPP): Energy that producers
capture by photosynthesis or other means (GPP, gross primary productivity), minus amount they lose as heat in cellular respiration
NPP = GPP - respiration
NPP varies among ecosystems and has a large impact on these systems
Ecology
• Energy moves through
ecosystems in a single
direction only — energy
cannot be recycled
• Nutrients are
continuously recycled
from the physical
environment to
organisms and back
again.
Ecology
Nutrient cycle
Cyclic movement of nutrients
such as nitrogen or
phosphorus between
organisms and the physical
environment
Life would cease if nutrients
were not recycled
• Likewise, life would cease if
energy stopped flowing
Answering Ecological Questions
Concept 1.3: Ecologists evaluate competing
hypotheses about natural systems with
experiments, observations, and models.
Jump to Slide 61
IRSC students in
Ecology lab near
Pruitt campus
Answering Ecological Questions
Ecologists use several methods to answer
questions about the natural world:
Observational studies in the field (comparative
field studies)
Controlled experiments in the laboratory
Manipulative experiments in the field
Quantitative models (computer, mathematical)
Jump to
Slide #55
Answering Ecological Questions
• An observational
(comparative) field study:
Johnson et al. (1999)
surveyed ponds to determine
that frogs with deformities
were only present if the
parasite’s intermediate host
snail was also present
http://www.converge.org.nz/nbio/images/sampling.jpg
Answering Ecological Questions
• A controlled experiment:
Johnson et al. (1999) also tested their
observations by exposing tadpoles to four
different levels of the parasite Ribeiroia in the
laboratory
Answering Ecological Questions
• A field experiment
Kiesecker (2002)
compared frogs from
three ponds containing
pesticides with frogs
from three ponds that
had no pesticides.
Valid manipulative field
experiments must also
have controls in the
experimental design
Answering Ecological Questions
Ecological experiments can
be done at different spatial
scales:
Small-scale laboratory
experiments in test tubes or
flasks, to whole-lake
experiments
When possible, experiments
include a control group,
which is not subjected to any
alterations.
Answering Ecological Questions
Sometimes experiments are
difficult or impossible to
perform
For example…questions
concerning events that occur
over large geographic and/or
time scales, such as global
climate change, El Niño
Possible approach: Conduct
observational studies over
large regions or for long time
periods (limited by lack of
control by researcher)
http://global-warming.accuweather.com/gissocean-thumb.gif
http://www.grida.no/climate/vitalafrica/english/graphics/11-tarmodel.jpg
…then data can be entered into mathematical models to
help understand the system under study
Answering Ecological Questions
The study of global
climate change involves
using a mixture of…
observational studies,
small-scale experiments,
and…
quantitative
(mathematical or
computer) models
http://www.m4gw.com:2005/m4gw/2008/07/cow_farts_collected_in_plastic.html
Scientists estimate that methane
from cows accounts for more
than 30% of Argentina’s total
greenhouse emissions. Methane
is 23 times more effective
trapping heat than CO2
Cow farts collected in
plastic tank for climate
change study
Concept 1.3
Answering Ecological Questions
Climate change: A directional change in
climate (such as global warming) that occurs
over 30 years or longer.
• Climate affects many aspects of ecology, and changes have
already occurred in the physiology, survival, reproduction,
and geographic ranges of hundreds of species.
http://www.earthgauge.net/2011/climate-fact-bird-breeding-range-shifts-great-lakes
Many species’ distributions are
shifting towards the poles already.
Swainson’s Thrush moved their
breeding range latitude 88 miles
farther north since the 1970s, while
the Blue-gray Gnatcatcher has
moved their breeding range 195
miles farther north over the same
period.
Layout of field showing
replicates of 5x5 meter
plots in two treatments
(with and without insect
removal) randomly
assigned
Answering Ecological Questions
Key aspects of good
experimental design:
• Replication
Perform each treatment more than
once
As number of replicates increases, it
becomes less likely that the results
were actually due to a variable that
was not measured or controlled
Increased sample size within
treatments decreases likelihood that
effects are due to chance alone
Answering Ecological Questions
Key aspects of good
experimental design:
• Randomization
• Assign treatments at random
• Helps limit effects of unmeasured
variables
• Standard statistical analyses are
used to determine significant effects
Layout of field showing
replicates of 5x5 meter
plots in two treatments
(with and without insect
removal) randomly
assigned
Answering Ecological Questions
Scientists learn about the natural world by a series of steps called the scientific method:
1.Make observations and ask questions.
2.Use previous knowledge or intuition to develop a testable hypotheses, i.e. a possible explanation (cause) of phenomenon (how or why)
3.Make a testable prediction based on hypothesis… what will happen (effect) if hypothesis is true, within context of study design
http://physics.ucr.edu/~wudka/Physics7/Notes_www/img1.gif
Answering Ecological Questions
• Example:
If Lake “O” nutrient-rich discharges cause plankton blooms in IRL…
then nutrient levels should be higher in IRL after discharges
then should detect increased blooms during times after discharges
http://physics.ucr.edu/~wudka/Physics7/Notes_www/img1.gif
Answering Ecological Questions
4. Evaluate hypotheses (i.e. are
predictions true) by examining
results of experiments, a
comparative observational studies,
or using quantitative models
5. Use results to modify the
hypotheses, to pose new
questions, or to draw conclusions
about the natural world
The process is iterative (repeats) and
self-correcting.
http://physics.ucr.edu/~wudka/Physics7/Notes_www/img1.gif
Answering Ecological Questions
Alternative hypotheses
• Different “explanations” for
phenomenon
• E.g. – parasites, pesticides, pollution,
UV radiation, habitat loss may
account for amphibian declines
• Hypotheses may be mutually
exclusive (single cause) or not
(multiple causes)
A scientific theory
From consistent results
Supported by lots of data, usually
from many different sources http://physics.ucr.edu/~wudka/Physics7/Notes_www/img1.gif
Case Study Revisited: Deformity and Decline in Amphibian
Populations
Studies have suggested that no single factor can
explain decline of amphibian populations.
Declines seem to be caused by complex factors that
often act together and may vary from place to place
The relative importance of factors such as habitat loss,
parasites, pollution, UV exposure, and others, are still
being investigated.
http://amphibiaweb.org/images/gaa_global_threatened_species.jpg
A Case Study Revisited: Deformity and Decline in Amphibian
Populations
• Stuart et al. (2004)
analyzed studies on 435
species:
Habitat loss was the
primary cause for 183
species; overexploitation
for 50 species.
The cause for the
remaining 207 species was
poorly understood.
http://sapiens.revues.org/1406
Case Study Revisited: Deformity and Decline in Amphibian
Populations
Hatch and Blaustein (2003) studied effects of UV light
and nitrate on Pacific tree frog tadpoles
At high elevation sites, neither factor alone had any affect
But together, the two factors reduced tadpole survival
At other low elevation sites, this effect was not seen
http://www.fs.fed.us/r4/amphibians/images/pacifictreefrog_tadpole2.jpg
Figure 1.14 Joint Effects of Nitrate and UV Light on Tadpole
Survival
Case Study Revisited: Deformity and Decline in Amphibian
Populations
The effects of pesticides are also complex…
Some studies (Relyea, 2003) show that tadpoles are
more susceptible when under stress, such as
presence of predators
http://www.chronicle.pitt.edu/wp-content/uploads/2007/08/ple-relea.jpg
Rick Relyea Studies Deadly Effects of
Pesticides (Roundup) on Amphibians
http://www.donrelyea.com/front_img/big_tadpole_large.jpg
A Case Study Revisited: Deformity and Decline in Amphibian
Populations
Skerrat et al. (2007) argued that some declines
may be due to pathogens
a chytrid fungus that causes a lethal skin disease
and has spread rapidly in recent years.
climate change and altered conditions may be
favoring growth and transmission of disease
organisms.
https://frogmatters.wordpress.com/category/chytrid-fungus/page/4/
Frog with chytrid fungal infection
(Batrachochytrium dendrobatidis
or Bd infection)
http://news.mongabay.com/2013/0919-watsa-chytrid-fungus-
devastates-salamanders.html
Case Study Revisited: Deformity and Decline in Amphibian
Populations
Amphibian declines seem to be caused by complex
factors that often act together and may vary from
place to place.
A broad set of factors can cause frog deformities, but
little is known about how these factors interact.
There remains much to be discovered in the field of
ecology.
Connections in Nature: Mission Impossible?
The natural world is vast,
complex, and
interconnected.
But ecologists think
that it is not impossible
to understand it.
Ongoing efforts are
sure to be challenging,
exciting, and important
to the well-being of
human societies.
http://www.payvand.com/news/08/jun/Earth-BlueMarble-NAASA.jpg